|Publication number||US7305894 B2|
|Application number||US 11/128,642|
|Publication date||11 Dec 2007|
|Filing date||13 May 2005|
|Priority date||14 May 2004|
|Also published as||CA2564391A1, CA2564391C, EP1753911A1, EP1753911B1, US20060020418, WO2005113892A1|
|Publication number||11128642, 128642, US 7305894 B2, US 7305894B2, US-B2-7305894, US7305894 B2, US7305894B2|
|Inventors||Robert Hunter Moore, David Murphy|
|Original Assignee||Stowe Woodward, L.L.C.|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (38), Non-Patent Citations (1), Referenced by (3), Classifications (12), Legal Events (6)|
|External Links: USPTO, USPTO Assignment, Espacenet|
This application claims the benefit of and priority to U.S. Provisional Application No. 60/571,174, filed May 14, 2004, and entitled Nip Width Measurement System, the disclosure of which is hereby incorporated herein by reference.
The present invention relates generally to the field of nip press technology and, more particularly, to systems and methods for measuring nip width between loaded rolls in a nip press.
In the process of papermaking, many stages may be required to transform headbox stock into paper. The initial stage is the deposition of the headbox stock onto paper machine clothing or felt. Upon deposition, the white water forming a part of the stock flows through the interstices of the felt, leaving a mixture of water and fiber thereon. The felt then supports the mixture, leading it through several dewatering stages such that only a fibrous web or matt is left thereon.
One of the stages of dewatering takes place in the nip press section of the papermaking process. In the nip press section, two or more cooperating rolls press the fibrous web as it travels on the felt between the rolls. The rolls, in exerting a great force on the felt, cause the web traveling thereon to become flattened, thereby achieving a damp fibrous matt. The damp matt is then led through several vacuum and dewatering stages.
The amount of pressure applied to the web during the nip press stage may be important in achieving uniform sheet characteristics. Variations in nip pressure can affect sheet moisture content and sheet properties. Excessive pressure can cause crushing of fibers as well as holes in the resulting paper product. Conventional methods addressing this problem have been inadequate, and thus, this problem persists in the nip press stage, often resulting in paper of poor quality, having uneven surface characteristics.
Roll deflection, commonly due to sag or nip loading, is a source of uneven pressure distribution. Rolls have been developed which monitor and alter the roll crown to compensate for such deflection. Such rolls usually have a floating shell which surrounds a stationary core. Underneath the floating shell are pressure regulators which detect pressure differentials and provide increased pressure to the floating shell when necessary.
Notwithstanding the problem of roll deflection, the problem of uneven loading across the roll length, and in the cross machine direction, persists because pressure is often unevenly applied along the roll. For example, if roll loading in a roll is set to 200 pounds per inch, it may actually be 300 pounds per inch at the edges and 100 pounds per inch at the center.
Conventional methods for determining a pressure distribution profile for a roll may involve the use of nip width sensors. Nip width measurements may be taken along the length of a roll and then processed to generate a pressure distribution profile. Unfortunately, conventional technology uses spaced sensors configured in such a way that they may not be able to detect certain nip width variations that occur over small spatial dimensions, such as those near the end of a nipped roll or those near regions having high temperatures. For example, the region just outside the sheet edge of calendar covers may be especially important. There is no sheet to insulate the calendar cover from the heated mating roll and the dub has not started to keep the roll materials separated. Thus, the calendar cover in the region just outside the sheet edge may become hot and expand radially due to thermal expansion. This region may have greater nip pressure because it is similar to a localized thicker region. Another example is where local damage or a local hot spot raises the cover.
According to some embodiments of the present invention, a system for determining characteristics of two rolls configured in a nip press includes a strip configured to be placed in the nip press. A plurality of sensors embedded in the strip is configured to generate signals representative of the pressure and/or the nip width between the two rolls. Interface circuitry facilitates addressing of individual ones of the plurality of sensors via a data processing system.
In other embodiments, the interface circuitry is embedded in the strip.
In other embodiments, the interface circuitry is attached to the strip.
In other embodiments, the plurality of sensors is configured in a plurality of sensor banks. The interface circuitry includes a plurality of multiplexer circuits respectively coupled to the plurality of sensor banks, each of the multiplexer circuits being responsive to a sensor address to select the output signal of one sensor contained on the respective sensor bank coupled thereto.
In other embodiments, a bank selection circuit is coupled to the plurality of multiplexer circuits and is responsive to a multiplexer selection address to selectively enable one of the plurality of multiplexer circuits.
In other embodiments, a plurality of processors is respectively coupled to the plurality of multiplexer circuits and is responsive to a multiplexer selection address to selectively enable one of the plurality of multiplexer circuits.
In still other embodiments, a data processing system is configured to process the signals and calculate values representative of the signals.
In still other embodiments, a display is coupled to the data processing system and is configured to provide a visual representation of the values.
In still other embodiments, the data processing system is configured to calculate measurements of nip width based on the signals.
In still other embodiments, the data processing system is configured to calculate measurements of nip width based on the signals at predetermined times.
In still other embodiments, a wireless transmitter is configured to communicate the signals to the data processing system.
In still other embodiments, a control system is communicatively coupled to the plurality of sensors and is configured to initiate corrective measures for the nip press responsive to the signals.
In still other embodiments, the plurality of sensors embedded in the strip is configured to generate signals that provide a substantially continuous representation of the pressure and/or the nip width along a length of the two rolls.
Although described above primarily with respect to system embodiments of the present invention, it will be understood that the present invention may be embodied as systems, methods, and/or apparatus.
Other features of the present invention will be more readily understood from the following detailed description of specific embodiments thereof when read in conjunction with the accompanying drawings, in which:
While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that there is no intent to limit the invention to the particular forms disclosed, but on the contrary, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the claims. Like reference numbers signify like elements throughout the description of the figures.
As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless expressly stated otherwise. It should be further understood that the terms “comprises” and/or “comprising” when used in this specification is taken to specify the presence of stated features, integers, steps, operations, elements, and/or components, but does not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. It will be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. Furthermore, “connected” or “coupled” as used herein may include wirelessly connected or coupled. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.
Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
The sensing system 1 comprises a strip 2, such as an elongated member made of a thin film of material. Sensors 4 are fixed to the strip for sensing pressure/force and/or nip width. The strip 2 having sensors 4 thereon is shown for purposes of illustration as not contacting the felt 8 and roll 6. During system operation, however, the strip 2 may lie in the nip between roll 5 and the felt 8 or directly between rolls 5 and 6. Placement of the strip 2 within the nip may be achieved by removably attaching the strip to roll 5, as shown, and then rotating roll 5 to properly position the strip. Alternatively, the strip may be may be placed directly between rolls 5 and 6 and rolled into the nip by rotating the rolls. The nip formed by rolls 5, 6 may also be opened and the strip placed between the rolls. The nip may then be closed.
The strip 2 having sensors 4 thereon may be rolled into a coil 15 for storage and unrolled during use. According to some embodiments of the present invention, the sensors 4 are spaced on the strip in sufficient numbers so that a substantially continuous distribution of pressure or nip width across the roll may be determined. The sensing system 1 can be used on any length roll, eliminating the need for different length sensing systems for different rolls and/or mills. Also, several strips of sensors may be pieced end-to-end to span the length of very long rolls.
In accordance with various embodiments of the present invention, the sensors 4 may comprise resistive, piezoelectric, piezoresistive, strain gage, and/or fiber optic materials. Also, the sensors may be equipped with temperature measuring sensors to aid in temperature compensation if needed.
In communication with the sensors 4 are associated electronics 10. The electronics 10 connected to the sensors 4 may aid in converting the sensor signals to pressure signals and/or nip width signals by amplifying the signals and/or eliminating external interference. The type of sensor used, however, determines the nature of the associated electronics 10. For example, if piezoelectric or piezoresistive sensors are used, the electronics 10 may comprise charge amplifiers. Alternatively, if strain gage sensors are used, the electronics 10 may comprise wheatstone bridges. If fiber optic materials are used, the electronics may comprise an optical phase modulator.
The electronics 10 are in communication with an input/output port 12, which is accessed by a bidirectional transmitter 14. The computer or data processing system 18 cycles through the sensors 4 to obtain pressure and/or nip width measurement signals from sensor locations along the strip 2 and, thus, along the roll 5 in the nip press. The bidirectional transmitter 14 transmits the signals from the multiplexer input/output port 12 to a signal conditioner 16 which, in turn, delivers conditioned signals representing the pressure and/or nip width sensed to the computer 18.
The sensors and associated electronics may be connected directly to the computer via wire cable. Nonetheless, the signals may be sent via telemetry or through slip rings. The computer 18 has a microprocessor having the ability to access the input/output port 12 at predetermined or requested times to obtain pressure-related and/or nip width-related data. Requested transmissions are achieved by operator input through the keyboard 19 of the computer. Once the computer 18 has indicated to the circuitry on the strip 2 which channels to read, the computer 18 receives the signals from the sensors 4 associated with the channels selectively accessed by the circuitry on the strip 2. Such signals are delivered to the microprocessor which runs a software program to compute a pressure value and/or nip width value. These values may then be transmitted to a display 20, which provides numerical or graphical cross machine pressure profiles and/or nip width profiles.
The computer 18 can further provide averages of the pressure and/or nip width values as well as initiate a correction signal to an optional control system 22. In addition, the computer 18 can determine nip widths indirectly from the pressure sensed and/or the measured sensor resistance through analysis software. The software takes the pressure signals and provides output data relating to nip width. This can also be accomplished through empirical relationships such as the ones used to relate nip width to line load or through experimentally obtained graphs. Various sensor types and their use in determining pressure and/or nip width are discussed in U.S. Pat. No. 6,205,369 to Moore, which is hereby incorporated herein by reference in its entirety.
The control system 22 can be connected to the computer 18 or the signal conditioner 16 to correct any sensed pressure and/or nip width irregularities by increasing or decreasing the force being applied by the roll or by increasing or decreasing the degree of contact between the rolls 5, 6. The control system 22 has an internal computer 26 for receiving user inputs in response to interpretation of pressure and/or nip width sensed or for receiving direct readings from the signal conditioner. The control system's computer 26, upon receipt of such signals, may initiate corrective measures to adjust the force being applied by the roll 2.
Turning now to
As shown in
Advantageously, the sensor interface circuitry 100 of
The outputs of the sensors may be provided to the I/O port 12 for communication back to the computer 18 in some embodiments. In other embodiments, the outputs of the sensors may be provided to processors 111 a, 111 b, 111 c, and 111 d, which may use a serial communication protocol, such as RS485 to communicate with the computer 18 or, alternatively, another serial protocol, such as RS232. Wireless and customer protocols may also be used. As shown in
In other embodiments, one or more temperature sensors may be associated with the sensor banks 114 a, 114 b, 114 c, and 114 d or sensors to improve temperature compensation when calculating the nip width. In accordance with various embodiments of the present invention, a temperature sensor may be associated with each bank and/or sensor, or, alternatively, one or two sensors may be used to obtain an average temperature that may be used in temperature compensation when calculating the nip width.
Operations of the sensing system 1 of
Another approach would be to load the rolls at the prescribed journal forces, and then feed the sensor strip 2 through the nip. The placement of the strip 2 may be achieved through a robotic arm or other automated equipment. In addition, the strip 2 could be attached lengthwise to one of the rolls or could be carried by the felt or web. The sensor readings would be acquired as the sensor passes through the nip.
At a predetermined, or at an operator-requested time, the computer 18 communicates with the bidirectional transmitter 14, which further communicates with the input/output port 12. The multiplexer 18 then cycles through the sensors 4 via the sensor interface circuitry 100 of
The sensing system, according to some embodiments of the present invention, may provide the operator with the ability to determine the pressure and/or nip width profile of a roll in one or more nips so as to diagnose the presence of unevenly applied roll forces. The various graphical representations may enable the operator to determine the pressure being applied, the location on the strip being indicative of the location along the length of the rolls, and whether or not it is abnormal. The strip may contain numerous sensors so as to provide a substantially continuous profile of pressure and/or nip-width along the length of the roll. Moreover, the strip may include sensor interface circuitry to facilitate acquisition of measurements from the sensors on the strip. Corrective measures may be initiated in response to unevenly applied forces.
In concluding the detailed description, it should be noted that many variations and modifications can be made to the preferred embodiments without substantially departing from the principles of the present invention. All such variations and modifications are intended to be included herein within the scope of the present invention, as set forth in the following claims.
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|U.S. Classification||73/862.55, 73/158, 73/159, 73/160|
|International Classification||D21F3/06, G01L5/00|
|Cooperative Classification||G01L5/0085, D21F3/06, B41F13/24|
|European Classification||D21F3/06, B41F13/24, G01L5/00M8C|
|11 Oct 2005||AS||Assignment|
Owner name: STOWE WOODWARD, L.L.C., VIRGINIA
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|3 Jun 2011||AS||Assignment|
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